The present invention relates generally to emitters for drip irrigation systems, and more particularly, to such emitters which are pressure compensating to apply controlled water distribution to vegetation at relatively low rates of flow while automatically compensating for varying pressures in the water supply system. The amount of water emitted remains substantially constant despite fluctuations in the supplied water pressure.
A drip irrigation system provides application of water to specific plant or root zone locations in controlled quantities. It is thereby possible to irrigate planted areas with substantially less water than is used by general broadcast sprinkler or flooding methods. However, if the same non-pressure compensating emitter is used at all drip locations, those emitters in the irrigation system which are subject to higher water pressure release more water. There is thus uneven water distribution.
In order to overcome this problem, pressure-compensating emitters were developed which allow a fairly uniform water flow over a range of water pressures within the irrigation system. The following U.S. patents disclose many of the typical techniques which are currently used:
______________________________________ U.S. Pat. No. Inventor(s) ______________________________________ 3,719,327 McMahan 3,767,124 Spencer 3,799,441 Delmer 3,804,334 Curry 3,833,176 Caldwell 3,876,155 Ruben 3,882,892 Menzel 3,899,136 Harmony 3,908,694 Spears 3,912,165 Pira 3,917,169 Harmony 3,934,824 Fitzhugh 3,954,223 Wichman et al. 3,993,248 Harmony 4,009,832 Tiedt 4,011,893 Bentley 4,023,595 Zakay 4,077,571 Harmony 4,132,364 Harmony 4,143,820 Bright, Sr. 4,147,307 Christy et al. 4,210,287 Mehoudar 4,235,380 Delmer 4,254,791 Bron 4,307,841 Mehoudar et al. 4,344,576 Smith 4,354,639 Delmer ______________________________________
These patents disclose the use of elements which restrict a flow path or distorts water outlets in order to limit the flow rate. Typically, a diaphragm or flexible membrane is disposed so that, in response to water pressure fluctuation, the diaphragm or membrane flexes into a region through which water flows. Thus, as water pressure increases, the membrane deforms into the corresponding flow channel, reducing the sectional area of flow path and restricting flow. The result is, if the emitter is properly designed, a generally uniform flow rate for a range of water pressures.
These types of emitters have some inherent problems. They are sensitive to clogging, because of sediment collecting in the restricted flow paths. Further, they typically utilize elastomeric or otherwise deformable material which is responsive to pressure applied to them. The membrane or diaphragm flexibility changes as a result of absorbing water. Also, during its operating period its flexibility or elasticity changes as a result of aging. These variations prevent the emitters from maintaining a constant output for the desired range of fluid pressures to which it is subject. The reliability and accuracy of the emitters is thereby adversely affected.